This study (open access) compared four different test approaches (DNA barcoding rbcL, DNA barcoding matK , ITS2 barcoding vs the NCBI database, ITS2 barcoding vs the BOLD database) in an authenticity survey of 100 herbal infusions on the Portuguese market. Samples included 94 single-species products and six polyherbal formulations.
The authors report that DNA extraction was successful for 94 samples, while six single-species products failed to amplify any of the tested barcodes. Among the 88 remaining single-species samples, ITS2 showed the highest amplification success (100 %), outperforming the barcodes rbcL (94 %) and matK (84 %).
Sanger sequencing confirmed the labelled species in 69.3 % of cases with rbcL and 48.9 % with matK. While 63 samples would be considered authentic solely based on barcoding (i.e., if either rbcL or matK matched the label), ITS2 metabarcoding revealed that many of these contained additional undeclared species, indicating that barcoding alone overestimated product authenticity. Of the 85 samples successfully analysed by ITS2 metabarcoding, only 27 (32 %) fully matched their label, while 58 (68 %) contained either additional undeclared species or complete substitutions. Several products contained undeclared species in significant proportions, indicating potential economic adulteration.
The authors conclude that their results revealed (i) the importance of curated and comprehensive databases, with a higher number of species being identified by NCBI database, (ii) the superior sensitivity of ITS2 metabarcoding, and (iii) the widespread mislabelling in commercial herbal products.
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